Flexible magnetic disk and method of making same

Abstract

A flexible magnetic disk is provided with a protective layer at the peripheral edge portion of the circular hole in the center of a magnetic disk sheet. The protective layer is formed by applying a radiation-polymerizable composition to the peripheral edge portion of the circular hole in the center of the magnetic disk sheet by letterpress printing, and exposing the composition to a radiation to cure the composition.

We claim: 
     
       1. A flexible magnetic disk provided with a protective layer at the peripheral edge portion of a circular hole in the center of a flexible magnetic disk sheet, said protective layer having a small coefficient of friction, and being formed by applying a radiation-polymerizable composition by letterpress printing and curing said radiation-polymerizable composition by exposure to a radiation, wherein said protective layer is formed in a doughnut shape having an inner diameter larger than the diameter of the circular hole in the center of the flexible magnetic disk sheet, and an outer diameter smaller than the diameter of the circular aperture in the center of a jacket for housing the magnetic disk sheet, and wherein said protective layer covers only the peripheral edge portion of said circular hole. 
     
     
       2. A method of making a flexible disk, which comprises the steps of: applying a radiation-polymerizable composition to a substrate web by letterpress printing, exposing said letterpress-printed composition to a radiation to cure said composition, punching said web into a doughnut shaped piece, and applying said piece to the peripheral edge portion of a circular hole in the center of a flexible magnetic disk sheet, thereby forming a protective layer having a small coefficient of friction, wherein said protective layer is formed in a doughnut shape having an inner diameter larger than the diameter of said circular hole in the center of said flexible magnetic disk sheet, and and outer diameter smaller than the diameter of the circular aperture in the center of a jacket for housing said magnetic disk sheet. 
     
     
       3. A method of making a flexible magnetic disk, which comprises the steps of: applying a radiation-polymerizable composition to only the peripheral edge portion of a circular hole in the center of a flexible magnetic disk sheet by letterpress printing, and then exposing said radiation-polymerizable composition to a radiation, thereby curing said radiation-polymerizable composition and forming a protective layer having a small coefficient of friction, wherein said protective layer is formed in a doughnut shape having an inner diameter larger than the diameter of said circular hole in the center of said flexible magnetic disk sheet, and an outer diameter smaller than the diameter of a circular aperture in the center of a jacket for housing said magnetic disk sheet. 
     
     
       4. A method as defined in claim 3 wherein said letterpress printing is conducted only on the peripheral edge portion of the circular hole in the center of said flexible magnetic disk sheet exposed from a circular aperture in the center of a jacket after said flexible magnetic disk sheet is housed in said jacket. 
     
     
       5. A method as defined in claim 3 or 4 wherein said exposure to the radiation is conducted on said letterpress-printed composition exposed from a circular aperture in the center of a jacket after said flexible magnetic disk sheet is housed in said jacket.